The present invention relates to a spin valve magnetoresistive effect type element assessment method and a spin valve magnetoresistive effect type element assessment device for assaying the magnetization state in a pinned layer in a spin valve magnetoresistive effect type element.
A spin valve magnetoresistive effect type element or an element called a spin valve element has been known as an element for a magnetic sensor.
The spin valve magnetoresistive effect type element is an element comprising, as shown in FIG. 10, a free layer 31 made of a ferromagnetic material (Nixe2x80x94Fe, etc.), an intermediate layer 32 made of a non-magnetic metal material (typically, Cu), a pinned layer 33 made of a ferromagnetic material (Nixe2x80x94Fe, etc.), and an antiferromagnetic layer 34 made of an antiferromagnetic material (Mnxe2x80x94Fe).
The spin valve magnetoresistive effect type element (hereinafter, referred to as the SV element) is an element that detects an external magnetic field by exploiting the fact that the element resistance varies considerably with a difference between the direction of magnetization in the free layer 31 and that in the pinned layer 33, and used as a magnetic data reading element in an magnetic disk device, a magnetic tape device, a magnetic card reader, etc., for example.
The antiferromagnetic layer 34 in the SV element is a layer that prevents the direction of magnetization in the pinned layer 33 from being dependent on an external magnetic field (fixes the direction of magnetization to the initial direction). The intermediate layer 32 is a layer that weakens the exchange interaction between the free layer 31 and pinned layer 33, and made thinner than the correlation length of conduction electrons. The free layer 31 is a layer, in which the direction of magnetization is free to change in response to an external magnetic field, and typically subjected to heat treatment in the magnetic field so as to have an easy axis that is perpendicular to the direction of magnetization in the pinned layer 33.
Thus, the SV element detects a difference between the direction of magnetization in the free layer 31 and that in the pinned layer 33 caused by an external magnetic field as variance in resistance. Therefore, detectability of magnetic field is affected considerably by the magnetization state in the pinned layer 33. Also, because the magnetization state in the pinned layer 33 is fixed by the antiferromagnetic layer 34, if a temperature raises above the Nxc3xa9el temperature at a portion within the antiferromagnetic layer 34, there may occur inconveniences such that the detectability of magnetic field is degraded, or the SV element no longer functions as the magnetic field detecting element.
More specifically, given that the magnetization state in the pinned layer 33 and the xcfx81-H characteristics of the SV element immediately after the manufacturing are as those shown in FIGS. 11(a) and 11(b), respectively, if the magnetization state in the pinned layer 33 changes to the one as shown in FIG. 12(a) in a use, then the xcfx81-H characteristics may change correspondingly to the one as shown in FIG. 12 (b). Further, if the direction of magnetization in the pinned layer 33 is completely inversed as shown in FIG. 13 (a), then the xcfx81-H characteristics of the SV element may change correspondingly to the one as shown in FIG. 13 (b).
As a preventive technique against such characteristics deterioration caused by a change of the magnetization state in the pinned layer 33, U.S. Pat. No. 5,650,887 discloses a magnetic disk device and a magnetic field sensor for, when the xcfx81-H characteristics of the SV element are deteriorated, providing the pinned layer with circumstances (magnetic field and temperature) capable of restoring the magnetization state to the initial state by allowing a current of a predetermined pattern to pass through.
According to the magnetic disk device disclosed in the above publication, deterioration of the xcfx81-H characteristics of the SV element provided in a magnetic head is detected by an increase in an error rate. Also, the magnetic field sensor detects deterioration of the xcfx81-H characteristics by a drop in an output from the sensor.
By using the aforementioned technique, it is possible to restore the characteristics of the SV element that have been deteriorated in response to a change of the magnetization state in the pinned layer. However, if the characteristics of the SV element are deficient from the start, it is impossible to upgrade such deficient characteristics to the standards. In other words, an SV element may be produced, in which the magnetization in the pinned layer 33 is not inversed, but the gradient of the xcfx81-H characteristics is smaller than a typical one.
Adapting the foregoing technique to such an SV element, however, cannot upgrade the characteristics of the SV element to the standards by means of current passing treatment. On the contrary, this causes a magnetic disk device or a magnetic field sensor to trigger the current passing treatment in response to a slight inversion of the magnetization (trigger the current passing treatment frequently). Also, incorporating a magnetic head employing such an SV element in a normal magnetic disk device could only result in a magnetic disk device with strong likelihood of becoming incapable of reading data.
The present invention is devised to solve the above problems, and therefore, has an object to provide a spin valve magnetoresistive effect type element assessment method and a spin valve magnetoresistive effect type element assayer, which can assessment the existence of an area in the pinned layer in the spin valve magnetoresistive effect type element where the magnetization has been inversed.
According to a spin valve magnetoresistive effect type element assessment method of the present invention, a resistance value of a spin valve magnetoresistive effect type element is measured while a relative location correlation between the spin valve magnetoresistive effect type element and a magnetic field having a predetermined intensity distribution is adjusted. Then, a magnetization state in a pinned layer in the spin valve magnetoresistive effect type element is assayed based on a correlation between the relative location correlation and resistance value obtained from measuring.
In other words, it is difficult to find directly the magnetization state (position, width, etc. of a portion where magnetization is inverted) in the pinned layer by the relative location correlation between the SV element and magnetic field and the correlation between the SV element and resistance value obtained from the foregoing measuring. However, it is easy to compute a correlation that would be measured by presuming the magnetization state in the pinned layer.
Hence, by measuring the relative location correlation between the SV element and magnetic field and the correlation between the SV element and resistance value like in the present invention, it is possible to presume the magnetization state and the width and position of a magnetization inverted area in the pinned layer from similarity with the correlation obtained by means of computation and the correlation obtained by means of measurement.
In addition, a spin valve magnetoresistive effect type element assessment device of the present invention is a device for assaying a magnetization state in a pinned layer in a spin valve magnetoresistive effect type element incorporated in a magnetic head, including: a magnetic disk having an assaying track, in which predetermined magnetic information is recorded; an actuator which maintains the magnetic head over the magnetic disk, the actuator also changes a distance between the magnetic head and a rotation center of the magnetic disk; and a position dependency data measuring and outputting unit which outputs position dependency data representing position dependency of a resistance value of the spin valve magnetoresistive effect type element by measuring the resistance value of the spin valve magnetoresistive effect type element while changing a position of the magnetic head in relation to the assaying track under control of the actuator.
According to the above spin valve magnetoresistive effect type element assayer, the SV element assessment method of the present invention can be adapted to an SV element incorporated in a magnetic head. In other words, because the magnetization state in the pinned layer in the SV element inside the magnetic head can be assayed, by using the present assayer, it becomes possible to judge, before the magnetic head is incorporated in a magnetic disk device, whether the magnetic head is normal or the magnetic head has normal characteristics due to heat treatment in the magnetic field, etc. Also, it becomes possible to effectively develop and conduct a study on a magnetic head that does not readily cause magnetization inversion in the pinned layer in the SV element and a magnetic disk device.
The position dependency data measuring and outputting unit is not limited to the type that measures the resistance value of the SV element per se, and can be of any type that measures a value equivalent to the resistance value. For example, it maybe a type that measures a current by applying a constant voltage to the SV element or a type that measures a voltage by supplying a constant current to the SV element. Also, an output form of the position dependency data can be a display on a display screen, print out on a sheet of paper, a formation of a file, etc.
When achieving the spin valve magnetoresistive effect type element assessment device of the present invention, the assaying track prepared on the magnetic disk can have any width. However, if it is arranged in such a manner that the assaying track is a track having a width narrower than a core width of the spin valve magnetoresistive effect type element subject to assaying, the spin valve magnetoresistive effect type element assessment device can be a device that outputs the position dependency data with which qualitative analysis is readily made. Magnetic information recorded in the assaying track is not especially limited. However, periodic magnetic information generally used in assaying the magnetic disk is preferable.
Also, when achieving the spin valve magnetoresistive effect type element assessment device of the present invention, a time variation data measuring and outputting unit which measures the resistance value of the spin valve magnetoresistive effect type element, and outputs time variation data representing time variation associated with measuring can be additionally provided. By preparing the assaying track where magnetic information that makes a dibit reproducing waveform obtainable is recorded on the magnetic disk when the time variation data measuring and outputting unit is additionally provided, in case that the magnetization is inverted in more than half the area in the pinned layer in the SV element, one can obtain time variance data that directly indicates the occurrence of the magnetization inversion.